High-frequency EMI radiated by electronic devices, noise above 1GHz, is attracting increased scrutiny; revisions to EMI standards have expanded the scope of regulated frequencies into the GHz waveband.
Electromagnetic interference (EMI) of 1GHz and above must be suppressed: EMI standards are getting increasingly tough with recent revisions, striving to minimize interference in the GHz communication wavebands used by mobile phones, Wireless Local Area Networks (LAN), global positioning system (GPS) and other systems. To start, regulations on EMI up through 6GHz will be implemented in Europe and Japan in Oct 2010, for printers and certain other items (Note 1). These new standards are based on CISPR22, issued by the International Special Committee on Radio Interference (CISPR*) in 2005. The upper limit of the regulated waveband for "information technology equipment," including printers, multi-function copiers and personal computers (PC), will be raised from 1GHz to 6GHz. And with CISPR22 to be implemented worldwide, starting with Europe and Japan, equipment manufacturers have to get ready.
Note 1: The unified European standard is EN55022. The EU Committee has issued an EMC Directive and member nations are drafting compliant regulations.
*CISPR: Comite International Special des Perturbations Radioelectrique
The movement to
tighten up regulations on EMI above 1GHz is gradually spreading to
encompass the entire electronics industry. CISPR22 covers information
technology equipment, but it has been merged with CISPR13 for
televisions and other broadcasting receivers, related equipment like
digital videodisc (DVD) recorders and more, to create the new CISPR32
standard (Fig 1). Applying to game systems, portable audio players,
electronic dictionaries and the like, it will cover just about all
consumer electronics.
The impact of raising the high end of the regulated waveband from 1GHz to 6GHz for electronic equipment EMI is significant (Fig 2). Many electronic products today mount integrated circuits (IC) and other devices with clock frequencies over 1GHz, but the existing CISPR standard does not regulate EMI of 1GHz or higher. As a result, explains one engineer in the electromagnetic compatibility (EMC) field, there are many products which have simply been "ignoring EMI of 1GHz or above until now" (Note 2).
Note 2: One cause of EMI is IC clock frequency. In addition to the fundamental frequency, harmonics can also become noise sources. Harmonic signals are integer multiples of the fundamental frequency. A third-order harmonic would be three times the fundamental frequency, and would often have significantly more energy. If the frequency clock signal is adjusted so that the third-order harmonic is outside the regulated waveband, then, it becomes easier to achieve compliance.
The revisions will spell trouble for "All high-speed serial transfers," warns one EMC engineer. The industry is especially concerned about internal connection interfaces such as Serial Advanced Technology Attachment (ATA), memory buses and other microprocessor peripheral circuits, and external interfaces including Universal Serial Bus (USB) and High-Definition Multimedia Interface (HDMI). Naturally, existing regulations on the waveband below 1GHz will remain in force, increasing the load on equipment developers.
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